In general, a broadcast station system compresses signals for digital broadcast, such as a video signal, an audio signal and a control signal, and transmits the compressed digital signals by using a digital television (DTV) transmitter. Here, the DTV transmitter transmits the compressed digital signals by using a radio channel assigned to the broadcast station system. Upon receipt of the compressed digital signals from the DTV transmitter, a DTV receiver decompresses the compressed digital signals, extracts video/audio signals from the decompressed signals and reproduces the extracted video/audio signals respective by its screen and speaker.
In the meantime, the DTV receiver is equipped with a tuner, and the tuner receives radio frequency (RF) signals through an antenna, converts the
RF signals into intermediate frequency (IF) signals and divides the IF signals into video signals and audio signals. According to modulation schemes, the tuner is divided into an analog tuner and a digital tuner, and the digital tuner is subdivided into a quadrature amplitude modulation (QAM) tuner for a cable broadcast, an orthogonal frequency division multiplexing (OFDM) tuner and a vestigial sideband (VSB) tuner for a terrestrial broadcast.
In the meantime, a digital broadcast system enables bi-directional communication between a service provider and an end user to thereby make it possible to enhance a security function and to reasonably collect viewing fees. For complete bi-directional communication, an out-of-band (OOB) tuner for transmitting data from the service provider to the end user and a return path tuner for transmitting data from the end user to the service provider should be provided to the digital broadcast system. The present invention is particularly directed to a function of the OOB tuner.
The prior art digital tuner allows a data transmission from the service provider to the end user by using a frequency band of 100 through 350 MHz different from that of audio/video signals. For this, the prior art digital tuner is equipped with an OOB output line through which signals of the above frequency band is outputted therefrom. However, the OOB output line is extended from one of output ports of a splitter, and an RF output signal of the splitter is outputted through the OOB output line. Accordingly, a set in which the digital tuner is installed should be equipped with a additional OOB mixer circuit for mixing the RF signal outputted through the OOB output line into an IF signal.
Also, the installation of the additional OOB mixer circuit in the set increases a manufacturing cost of the set and makes it difficult to manufacture the set.